1. Field of the Invention
The present invention relates to an improved concept for a skid made of a polymeric material and consisting of a hollow profile. The skid is intended to be used with or constitute a part of a pallet, a container pallet or the like which preferably is made of a polymeric material and which is intended for transport and/or storage of goods.
2. Discussion of the Prior Art
A pallet or the like must, to be possible to convey on ball tracks or the like, downwards be provided with skids in order to eliminate the risk that it jams in for instance the ball track. Pallets or the like provided with skids, wherein the skids and preferably also the pallet are made of a polymeric material by injection moulding are disclosed in a large amount and with varying designs and functions. A skid can sometimes be for instance a solid profile formed as a lath or edging or be a hollow profile comprising a preferably closed longitudinal chamber. A hollow profile exhibits advantages such as being material saving and chock dampening, but known concepts comprising a single hollow chamber exhibit disadvantages such as reduced stability and/or reduced carrying capacity, for instance due to the resulting design of the longitudinal chamber. A disproportional ratio between the width and the height of the chamber renders the upper central area of the skid a tendency to bend downwards or inwards when charged. Furthermore, the material thickness of the chamber walls tends to be uneven. The difference in wall thickness between respective long and short sides of the skid and most of all the edges, with the weakest spots, becomes so large that strains reducing the strength, impact resistance, flexibility and stability of the polymeric material and/or resulting in a cracking, whereby the weakest spots are further weakened. The strains caused by material thickening, appears most of all at the edges and can be referred to the fact that the core temperature of the polymer after injection moulding exceeds the surface temperature to such an extent that the core shrinkage is larger than corresponding surface shrinkage. The difference in shrinkage results in a strong inner tension. Above disclosed properties give pallets provided with such polymeric skids a limited utilization.
A hollow profile is produced through injection moulding of a polymeric material using a gas injection procedure. One type of gas injection procedures involve a moulding tool having a rigid and defined moulding cavity which is entirely filled with a molten polymeric material. The moulding tool, furthermore, comprises one or more inlet channels enabling injection of gas into the core of the molten polymeric material and one or more outlet channels through which excess of molten polymeric material during injection of gas is evacuated out of the moulding cavity, whereby a substantially closed chamber constituting a hollow profile is formed. In an alternative procedure, a moulding tool with one or more variable moulding cavities, having one or more inlet channels for gas injection, is used. The moulding cavity is in this case provided with at least one movable element, which can be moved in or out, whereby the volume of the moulding cavity increases or decreases. Molten polymeric material is injected into the moulding cavity when the movable element is in such a position that the volume of the moulding cavity is decreased to a defined filling of molten polymeric material. The movable element is, in conjunction with the gas injection, moved outwards to a defined expansion of the moulding cavity, whereby a substantially closed hollow profile is formed.
Commonly used gas injection procedures and companies of origin include:
AIRMOLD--Battenfeld
AIRPRESS--Klockner Ferromatik
CINPRES (Contr. Internal Pressure Moulding)--Pearless Cinpress
ENCORE (Engineered Nitrogen Coresystem)--Encore Systems
GAIN (Gas-assisted Injection Molding)--Detroid Plastic Molding
GASMELT--Engel
GID (Gasinnendruckverfahren)--Dynamit-Nobel
GIP (Gasinnendruckproze.beta.)--Demag
GIT (Gasinjektiontechnik)--Schade